This invention relates to a photosensitive body, a developing unit having the photosensitive body, and an image forming apparatus having the photosensitive body and the developing unit.
Electrophotographic technology is recently widely used and applied not only in a field of copying machines but also in a field of various printers, since conventionally high quality images can be instantly obtained. Regarding a photosensitive body, which is a core element of the electrophotographic technology, as a photoconductive material thereof, the photosensitive body using an organic photoconductive material, having advantages such as, e.g., non-polluting and easy to deposit and to fabricate, prevails nowadays. Among an organic photosensitive body, a functionally separated type photosensitive body, in which a charge generation layer and a charge transport layer are layered, is widely prevalent. The functionally separated type photosensitive body has become mainstream of the photosensitive body, because a sensitive photosensitive body can be obtained by combining not only an efficient charge generation substance but also an efficient charge transport substance, because a highly safe photosensitive body can be obtained due to an availability of a wide range of materials, and because the functionally separated type photosensitive body is relatively advantageous in cost due to high coating efficiency. Regarding an electrostatic latent image formation mechanism of the functionally separated type photosensitive body, first, the light irradiates a charged photosensitive body to pass through the charge transport layer, and is absorbed by a charge generation substance in the charge generation layer, thus generating charges. Subsequently, the generated charges are injected into the charge transport layer at an interface between the charge generation layer and the charge transport layer, and is further moved by an electric field in the charge transport layer toward an outermost surface, then forming an electrostatic latent image by neutralizing surface charges on the photosensitive body. Recently, demand for a higher quality image formed in an electrophotographic process is further increasing. To realize this demand, it is necessary to prevent dispersion of electrostatic latent images in a photosensitive layer, and to improve reproducibility of thin lines and minute dots. Such a photosensitive body is specifically described in Japanese Unexamined Patent Publication No. Sho 59-044054.
However, the organic photosensitive body is easily worn by repeated use, and develops a strong tendency for further progression of charge potential drop, luminous sensitivity deterioration, and density drop of the photosensitive body, or image degradation such as, e.g., background fogginess due to deteriorating progression of photosensitive layer wear. In other words, there raises a problem that photosensitive body's durability cannot be maintained where the photosensitive layer is made thinner. Recently, higher durability of the photosensitive body is increasingly demanded because of a smaller diameter of the photosensitive body due to speed up or a smaller size of the image forming apparatus.
This invention is made in consideration of the above described problem, and it is an object of this invention to provide a photosensitive body having a thinner photosensitive layer while preventing duration deterioration that may occur with the thinner photosensitive layer, a developing unit having the photosensitive body, and an image forming apparatus having the photosensitive body and the developing unit.